This invention relates to water heaters, particularly to improvements to gas fired water heaters adapted to render them safer for use and to reduce NOx emissions.
The most commonly used gas-fired water heater is the storage type, generally comprising an assembly of a water tank, a main burner to provide heat to the tank, a pilot burner to initiate the main burner on demand, an air inlet adjacent the burner near the base of the jacket, an exhaust flue and a jacket to cover these components. Another type of gas-fired water heater is the instantaneous type which has a water flow path through a heat exchanger heated, again, by a main burner initiated from a pilot burner flame.
For convenience, the following description is in terms of storage type water heaters but the invention is not limited to this type. Thus, reference to xe2x80x9cwater container,xe2x80x9d xe2x80x9cwater containment and flow means,xe2x80x9d xe2x80x9cmeans for storing or containing waterxe2x80x9d and similar such terms includes water tanks, reservoirs, bladders, bags and the like in gas-fired water heaters of the storage type and water flow paths such as pipes, tubes, conduits, heat exchangers and the like in gas-fired water heaters of the instantaneous type.
A particular difficulty with many locations for water heaters is that the locations are also used for storage of other equipment such as lawn mowers, trimmers, snow blowers and the like. It is a common procedure for such machinery to be refueled in such locations.
There have been a number of reported instances of spilled gasoline and associated extraneous fumes being accidently ignited. There are many available ignition sources, such as refrigerators, running engines, electric motors, electric and gas dryers, electric light switches and the like. However, gas water heaters have sometimes been suspected because they often have a pilot flame.
Vapors from spilled or escaping flammable liquid or gaseous substances in a space in which an ignition source is present provides for ignition potential. xe2x80x9cExtraneous fumes,xe2x80x9d xe2x80x9cfumesxe2x80x9d or xe2x80x9cextraneous gasesxe2x80x9d are sometimes hereinafter used to encompass gases, vapors or fumes generated by a wide variety of liquid volatile or semi-volatile substances such as gasoline, kerosene, turpentine, alcohols, insect repellent, weed killer, solvents and the like as well as non-liquid substances such as propane, methane, butane and the like.
Many inter-related factors influence whether a particular fuel spillage leads to ignition. These factors include, among other things, the quantity, nature and physical properties of the particular type of spilled fuel. Also influential is whether air currents in the room, either natural or artificially created, are sufficient to accelerate the spread of fumes, both laterally and in height, from the spillage point to an ignition point yet not so strong as to ventilate such fumes harmlessly, that is, such that air to fuel ratio ranges capable of enabling ignition are or are not reached given all the surrounding circumstances.
One surrounding circumstance is the relative density of the fumes. When a spilled liquid fuel spreads on a floor, normal evaporation occurs and fumes from the liquid form a mixture with the surrounding air that may, at some time and at some locations, be within the range that will ignite. For example, the range for common gasoline vapor is between about 2% and 8% gasoline with air, for butane between 1% and 10%. Such mixtures form and spread by a combination of processes including natural diffusion, forced convection due to air current drafts and by gravitationally affected upward displacement of molecules of one less dense gas or vapor by those of another more dense. Most common fuels stored in households are, as used, either gases with densities relatively close to that of air (e.g. propane and butane) or liquids which form fumes having a density close to that of air, (e.g. gasoline, which may contain butane and pentane among other components, is very typical of such a liquid fuel).
In reconstructions of accidental ignition situations, and when gas water heaters are sometimes suspected and which involved spilled fuels typically used around households, it is reported that the spillage is sometimes at floor level and, it is reasoned, that it spreads outwardly from the spill at first close to floor level. Without appreciable forced mixing, the air/fuel mixture would tend to be at its most flammable levels close to floor level for a longer period before it would slowly diffuse towards the ceiling of the room space. The principal reason for this observation is that the density of fumes typically involved is not greatly dissimilar to that of air. Combined with the tendency of ignitable concentrations of the fumes being at or near floor level is the fact that many gas appliances often have their source of ignition at or near that level.
Earlier efforts, such as those disclosed in U.S. Pat. No. 5,797,355, substantially raised the probability of successful confinement of ignition of spilled flammable substances from typical spillage situations to the inside of the combustion chamber. Other following structures, such as those disclosed in U.S. Pat. Nos. 5,950,573; 6,003,477; 6,082,310; 6,085,699; and 6,085,700, for example, have built on the break through success of ""355.
Although the water heaters described in the above-identified patents have been well received and highly successful with respect to increasing the resistance to ambient flammable vapors, certain portions of the U.S., especially California, have stringent low NOx emissions regulations and requirements. We have discovered an ongoing challenge associated with meeting these limits with such structures. Accordingly, it has been a primary objective to produce a water heater that simultaneously addresses the issue of resistance to flammable vapors and can meet ever increasingly stringent low NOx emissions regulations and requirements by the various regulatory bodies.
One attempt to limit NOx emissions is U.S. Pat. No. 5,645,413 to Benedek et al., which discloses a water heater designed to operate with unlimited burner primary air, and a key feature is to recirculate secondary air to the primary combustion flame region. In ""413, the flame guide and burner are an integral system such that the burner does not function separately from the flame guide.
This invention relates to a water heater including a water container and a combustion chamber adjacent the container. The combustion chamber has a side wall and at least one flame arrestor to admit air and extraneous fumes into the combustion chamber and confine ignition and combustion of the extraneous fumes within the combustion chamber. A burner having a multiplicity of burner ports is associated with the combustion chamber and arranged to combust fuel to heat water in the container.
An air diverter including a substantially flat plate having a central opening larger than the diameter of the burner is positioned in the combustion chamber and below the burner ports in the burner. The plate is sized to create a gap between its outer edge and the side wall and is adapted to channel combustion air passing through at least a portion of the flame arrestor through the gap. A flange is positioned above the air diverter and has a central opening of a size and alignment substantially the same as that of the air diverter and the flange is angled upwardly and away from the air diverter in the radially outwardly direction and is positioned relative to the burner ports such that burner flames tend to attach thereto.